In wireless systems, a base station communicates with a wireless device by transmitting information to the wireless device on a downlink channel and receiving information from the wireless device on an uplink channel. Because many wireless devices may be trying to send information to the base station at the same time, a mechanism is provided to control which wireless device may transmit on the uplink to the base station during a specified time slot. This mechanism includes transmitting, to a wireless device, a grant sequence of bits that informs the wireless device that the wireless device is selected for uplink transmission. The grant sequence is typically transmitted to the wireless device via a dedicated channel.
The enhanced dedicated channel (E-DCH) Absolute Grant Channel (E-AGCH) is a fixed rate (30 kbps, SF=256) downlink physical channel that carries uplink E-DCH absolute grants for uplink E-DCHs associated with the E-AGCH set by higher layer signaling. As used herein, higher layer signaling means signaling at an open system interconnect (OSI) layer higher than OSI layer 2. FIG. 1 illustrates the frame 2 and sub-frame 4 structure of the E-AGCH. An E-DCH absolute grant is transmitted over one E-AGCH sub-frame 4 or one E-AGCH frame 2, depending on the E-DCH transmission time interval (TTI) to be used by a wireless device such as a user equipment (UE). The TTI can be set either to 2 ms or 10 ms. The Absolute Grant Value is transmitted using the E-AGCH. The Absolute Grant Value consists of 5 bits Xagv,1, Xagv,2, . . . , Xagv,5. In addition a 1 bit Absolute Grant Scope, Xags,1, is appended to these five bits.
The Absolute Grant Value information is specified in tables that are selected by higher layer signaling and which indicate how to perform the mapping of an index described in terms of bits to a power ratio. The Absolute Grant Scope is an activation flag used for (de)activating individual hybrid automatic repeat request (ARQ). The Absolute Grant Value information Xagv,1, Xagv,2, . . . , Xagv,5 and the Absolute Grant Scope information Xags,1 are multiplexed together. This gives a sequence of bits Xag,1, Xag,2, Xag,6 whereXag,k=Xagv,k k=1,2, . . . , 5Xag,k=Xags,7-k k=6  (1)
The E-RNTI stands for the E DCH Radio Network Temporary Identifier, and is mapped such that xid,1 corresponds to the most significant bit (MSB). From the sequence of bits Xag,1, Xag,2, . . . , Xag,6 a 16 bit cyclic redundancy code (CRC) is calculated. That gives the sequence of bits c1, c2, . . . , c16 whereck=Pim(17-k) k=1,2, . . . ,16This sequence of bits is then masked with xid,1, xid,2, . . . , xid,16 and appended to the sequence of bits Xag,1, Xag,2, . . . , Xag,6 to form the sequence of bits y1, y2, . . . , y22 whereyi=Xag,i i=1,2, . . . ,6yi=(ci−6+xid,i−6) mod 2 i=7, . . . ,22  (2)
Rate ⅓ convolutional coding is applied to the sequence of bits y1, y2, . . . , y22, resulting in the sequence of bits z1, z2, . . . , z90. From the input sequencez1,z2, . . . ,z90  (3)the bits z1, z2, z5, z6, z7, z11, z12, z14, z15, z17, z23, z24, z31, z37, z44, z47, z61, z63, z64, z71, z72, z75, z77, z80, z83, z84, z85, z87, z88, z90 are punctured to obtain the output sequencer1,r2, . . . ,r60.  (4)
The sequence of bits r1, r2, . . . , r60 is mapped to the corresponding E-AGCH sub frame. The bits rk are mapped so that they are transmitted over the air in ascending order with respect to k. If the E-DCH TTI is equal to 10 ms the same sequence of bits is transmitted in all the E-AGCH sub frames of the E-AGCH radio frame.
Thus, to recover the grant bit sequence, a receiving wireless device must de-puncture and decode the received signal on the E-AGCH.
On the secondary carrier, the UEs are supposed to transmit sequentially by following a time division multiplex (TDM) operation. The TDM operation can be performed by using the legacy E-AGCH. However, the following disadvantages have been identified:                Signaling Overhead: two E-AGCHs must be signaled, one for starting the data transmission, and one more for stopping the data transmission;        Scheduling Efficiency: the above activation/deactivation signaling overhead leads to a gap between the data transmissions of different UEs; and        Serious consequences arise from missed detection of the terminating grant, such as collisions of uplinks from multiple wireless devices.        
Methods have been proposed to avoid the drawbacks found in legacy systems. For example, when a grant is sent, the wireless device, e.g., user equipment (UE) keeps quiet and does not transmit if the CRC of the detected message is incorrect, otherwise the wireless device can start the transmission and continue transmission until detecting an incorrect CRC in the grant. In particular, the method consists of sending the grant information to a certain wireless device to indicate that the wireless device can start its uplink transmission. Then, discontinuous transmission (DTX) is used until another wireless device has to be granted.
When a wireless device detects that a grant for uplink transmission is for the wireless device, then the wireless device can start transmitting in the uplink. If the wireless device detects that a grant is sent for another wireless device, then the wireless device should stop transmitting immediately. Note that the terms “wireless device” and “UE” may be used herein interchangeably to denote a wireless device such as a mobile phone, computer, tablet computer, iPad, and the like. Embodiments are not limited to devices such as mobile phones.
Currently, requirements for the E-AGCH are defined only in terms of missed detection probability. According to this method, the UE transmits only if successful decoding of the grant occurs, while the wireless device stops transmitting if the wireless device detects that a grant was sent to someone else. Let:
Case A=wireless device ‘U’ successfully decodes its grant;
Case B=The E-AGCH is in DTX;
Case C=The NodeB transmits the grant for wireless device ‘U’; and
Case D=The NodeB transmits the grant for wireless device ‘K’. Several important events can occur as follows:                Missed detection: 1—Pr(A|C) corresponds to the usual missed detection probability, i.e. the wireless device ‘U’ cannot correctly detect its grant and hence the wireless device U does not start transmitting. This is linked to the CRC length, hence the missed detection probability is considered to be sufficiently low.        Wrong grant detection probability: Pr(A|D). This probability corresponds to the case when the wireless device ‘U’ decodes that a grant is sent for wireless device U when the network instead was transmitting a grant aimed for another wireless device. This condition happens with very low probability as again it is linked to the CRC length and the use of the E-RNTI as a mask. When this event happens, it can create a collision in uplink between 2 users.        False alarm probability: Pr(A|B). This corresponds to the conditional probability that the wireless device ‘U’ detects its grant given that no grant has been transmitted. This metric is already defined and the same requirement could be considered as valid also for this method. This probability is again linked to the CRC length and it is considered to be sufficiently small. However the corresponding complementary probability can be very high, 1—Pr(A|B). The complementary probability can be considered as the sum of two events, i.e.:        
(1) the wireless device detects that nothing is transmitted (and hence it continues its uplink transmission if the wireless device was transmitting) even though nothing has been transmitted
(2) the wireless device detects that a grant is sent to someone else given that nothing has been transmitted (and hence the wireless device stops its uplink transmission if the wireless device was transmitting)
In particular, for event (2), if the corresponding probability is not sufficiently negligible, this may lead to several interruptions in the wireless device transmission with negative consequences on the overall achieved throughput. There is a large potential probability during DTX that the wireless device wrongly detects that a grant is sent for another wireless device, which would lead to frequent wrong interruption of its uplink transmission.